Extruders for producing fiber-reinforced resin structures through a thermoplastic pultrusion operation are known in the art. Such extruders typically include the combination of a thermoplastic pultrusion impregnation chamber (known as a wet-out die in the art), a faceplate mounted over the downstream end of the chamber, and a roving puller located downstream of the faceplate. The impregnation chamber includes a slot-like channel through which string-like bundles of reinforcing fibers (hereinafter referred to as rovings) are impregnated with molten thermoplastic resin. The faceplate may include a plurality of sizing holes (sometimes referred to as shaping holes) or a single slot through which resin-impregnated rovings from the impregnation chamber are drawn, depending upon the type of faceplate used. The roving puller pulls the rovings through the die channel and the sizing holes or slot of the faceplate. In operation, hot, pressurized molten resin is continuously introduced into the channel as the rovings are pulled through the channel and through the faceplate by the puller. The resin-impregnated rovings are pultruded in parallel through the sizing holes or single slot of the faceplate to form elongated, fiber-reinforced structures whose cross-sectional shapes are defined by shape of the opening or openings in the faceplate. While sizing holes can have any one of a number of different shapes, they are typically round or slot-shaped and consequently produce pultrusions that are rod-shaped or ribbon-shaped in cross-section. Faceplates having a single slot produce a single sheet-shaped pultrusion. As the thermoplastic resin component of the pultrusions is still at least semi-molten immediately after the pultrusions are drawn from the sizing holes, the pultrusions may easily be further shaped into a desired final product. For example, if the final product is to be fiber-reinforced tape, parallel rod-like pultrusions exiting the faceplate may be squeezed between the nip of a pair of parallel rollers to form a resin sheet reinforced by a parallel array of fibers. After cooling, the sheet may be cut parallel along the fibers into strips to form a fiber-reinforced tape.
When making fiber-reinforced tape, it is desirable that the final product have a relatively high volume (i.e. >50%) of reinforcing fibers relative to the thermoplastic resin in order to have a high tensile strength. However, the applicants have observed that it is difficult to efficiently produce high fiber volume tapes with conventional extruders. Specifically, the applicants have found that the shaping holes or slot in the faceplate frequently become plugged with broken or loose fibers when the fiber volume of the resin/fiber mix pultruded through shaping holes exceeds 50%. When the sizing holes become partially plugged with such fiber debris, it can damage the roving, thereby degrading the tensile strength and hence the quality of the final product. Worse yet, such partially plugged holes often continue to accumulate fiber debris, which can result in the breakage one or more of the ravings. Should this occur, the extruder produces only scrap until the broken roving is replaced. Of course, the replacement of such a broken roving can only be achieved by shutting down production and restringing a roving through the wet-die and the formerly-plugged sizing hole of the faceplate.
The applicants have further observed that such undesirable plugging of the sizing holes is exacerbated when highly viscous thermoplastics of high molecular weight are used. Such viscous thermoplastics must be continuously subjected to relatively high pressures within the pultrusion impregnation chamber if they are to completely impregnate the rovings being pulled therethrough, and are subject to pressure surges during the operation of the extruder as a result of imbalances between the amount of thermoplastic being introduced into the chamber and the amount being withdrawn from the chamber by the resin impregnated rovings. During such surges, the resulting higher pressure of the resin in the sizing holes encourages loose or broken fibers from the roving to partially plug the holes, which in turn causes the resin pressure to further spike, thereby further promoting the plugging of the sizing holes. Such pressure surges normally do not occur, as the operators of the extruder are careful to balance the volume of the molten resin and roving moving through the die with the volume of the rods or ribbons pultruded through the sizing holes of the faceplate. However, small surges of a few pounds per square inch are unavoidable with present extruders during a production speed-up operation or a roving change-over operation. The applicants have observed that even a small pressure surge of 5% above normal can initiate the aforementioned plugging negative feedback loop when high fiber volume structures are being produced.
Clearly, there is a need for an extruder capable of continuously producing reinforced resin structures having fiber volume contents of 50% or greater without the plugging of the faceplate sizing holes even during pressure surges in the resin.
Further, problems exist with presently known fiber reinforced tapes, such as those generated by conventional extruders, in many applications, such as subsea applications. For example, tapes may be wrapped around existing products, such as pipe sections, to reinforce the pipe sections. However, presently known tapes may not adequately bond with such products to provide sufficient reinforcement.
As such, a need currently exists for an improved fiber reinforced polymer tape and method for forming a polymer reinforced polymer tape. Specifically, a need currently exists for tapes methods that provide improved bonding properties. Additionally, such tapes may provide the desired strength, durability, and temperature performance demanded by particular applications.